1. Field of the Invention
This invention relates to a vibration wave driven motor, more specifically an ultrasonic motor having large output, wherein a traveling vibration wave is produced by impressing applying an electric voltage over electro-mechanical energy conversion elements. The traveling vibration wave thus produced creates frictional driving between the vibrating body and a member that contacts the vibrating body, thereby producing relative movement.
2. Related Background Art
With a vibration wave driven motor of the prior art, especially of the large output type an array of piezo-electric elements arranged in a thin ring is fixed on a circular vibrating body base made of, for example, stainless steel. The surface of said the vibrating body base is thermally sprayed and deposited with ultra hard materials consisting of tungsten carbide and cobalt. The same surface is then finished by grinding to make a rigid sliding surface, thus constituting a vibrating body. In order to constitute a member that contacts the vibrating body, on the other hand, a supporting body made of, for example, aluminum alloy is used. Adhered to this supporting body are reinforced compound resin layers, wherein reinforcement materials such as carbon fiber are filled and mixed in the thermoplastic resins having a transition temperature to glass higher than 100.degree. C. including polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polyether etherketone (PEEK), polyether sulfone (PES), polyarylate (PAR), polysulfone (PSF), and heat resisting resins such as aromatic polyester of crystalline liquid (LCP), and the thermosetting aromatic polyimide (PI). A member processed this way makes a rigid sliding body. Such vibrating body and the contacting member are arranged so as to make relative movement by the frictional driving created by the traveling vibration wave that is produced in the vibrating body.
To create the relative movement mentioned above, either of the contacting member and the vibrating body can be arranged fixedly or movably. In the explanations hereinbelow in this specification, it is assumed that the vibrating body is fixedly arranged while the contacting member is set movable in order to make explanations simple. Consequently, the member that contacts the vibrating body is called "a movable body".
With the conventional vibration wave driven motor mentioned above, the reinforced thermoplastic resin having a transition temperature to glass higher than 100.degree. C. and the sliding body using thermosetting aromatic polyimide resin as the matrix are used for the reason that their physical property characteristics show a small degree of dependence on ambient temperature. Even when the temperature rises as a motor is being driven, the phenomenon of the torque drop due to softening of resin materials can be neglected, thus allowing the stable accuracy of the motor to be maintained.
Moreover, reinforcement materials such as carbon fiber are mixed and filled inside the above mentioned resin materials for the following reasons: (1) to maintain the stability of the sliding surface conditions of a movable body against the sliding surface of a vibrating body made of ultra hard materials of tungsten carbide and cobalt, and at the same time to guarantee enough wear resistance in the driving of long hours; (2) to improve a motor in its performance such as its output, by increasing the physical property values including elastic modulus or hardness of a sliding body; and (3) to improve a motor in its performance, such as its efficiency, and others points by enhancing the thermal conduction of the sliding body.
As described above, the use of the reinforcement type compound resin (wherein carbon fiber is filled in the heat resisting thermoplastic resin having a transition temperature point to glass higher than 100.degree. C. as well as the thermosetting polyimide resin) together with a sliding body (that constitutes a sliding surface for a movable body in the vibration wave driven motor) can stabilize the performance as well as the accuracy of a motor when temperature rises with a motor being driven. It also can provide the carbide materials forming a sliding surface of a sliding body with enough abrasion resistance for long hours of driving and further enables the motor performance such as its output efficiency to be enhanced to higher values.
With the sliding surface, however, of the above-mentioned carbon fiber reinforced compound resin layers (composed of the heat resisting thermoplastic resin and thermosetting aromatic polyimide resin) of a movable body and the surface pressed to and contacted with the rigid sliding surface composed of carbide materials of a vibrating body, a rated operation condition of 4 kg/cm, 100 rpm was used to start driving, and about 5% torque fluctuation in the rated torques value was observed. Accordingly, further improvements are desirable.
When driving was conducted over a long period of 1,000 hours under a comparatively high output condition of the rating, it was found that even the carbon-fiber reinforced compound resin wore was worn by more than 3 micron meters ( .mu.m). This suggests that further improvements of the abrasion resisting materials are desirable.